1. Field of the Invention
The present invention relates to a communication system, and more particularly to a data transmission/reception method for improving the use efficiency of resources in a communication system which transmits/receives data using limited resources.
2. Description of the Related Art
In a next-generation communication system, much research has been made to provide users with high-speed services with various qualities of service (QoS). Particularly, in the current next generation communication system, research is being vigorously pursued to support high-speed services for broadband wireless access (BWA) communication systems such as wireless local area network (WLAN) communication systems and wireless metropolitan area network (WMAN) communication systems by ensuring both mobility and various QoSs. A typical communication system for this purpose is the IEEE (Institute of Electrical and Electronics Engineers) 802.16a/d communication system and the IEEE 802.16e communication system.
The IEEE 802.16a/d and IEEE 802.16e communication systems, each of which is one of the BWA communication systems, are communication systems which apply an Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme in order to support a broadband transmission network to a physical channel of the WMAN system. The IEEE 802.16a/d communication system currently considers only the fixed state of a subscriber station (SS), that is, a state in which mobility of the SS is not taken into account at all, and considers only a single cell structure. In contrast with this, the IEEE 802.16e communication system reflects the mobility of an SS in addition to the characteristics of the IEEE 802.16a/d communication system. Hereinafter, the SS having mobility will be referred to as a mobile station (MS).
The IEEE 802.16e communication system, one of the BWA communication systems, has a frame structure, a base station (BS) of the system efficiently allocates resources of each frame, which are to be used by MSs, to the MSs, and the BS transmits resource allocation information to the MSs through MAP messages. Of the MAP messages, an MAP message used for transmitting downlink resource allocation information is a downlink-MAP (DL-MAP) message, and an MAP message used for transmitting uplink resource allocation information is an uplink-MAP (UL-MAP) message.
If the BS transmits downlink resource allocation information and uplink resource allocation information to the MSs through DL-MAP and UL-MAP messages in this way, the MSs can detect the positions of resources allocated thereto and control information of data to be received by the MSs themselves by decoding the DL-MAP and UL-MAP messages transmitted from the BS. By detecting the resource allocation positions and the control information, the MSs can transmit/receive data over the downlink and uplink.
The MAP message is configured in different MAP information element (IE) formats according to whether it is a DL-MAP message or a UL-MAP message and according to the type of a data burst, that is, according to whether a data burst is a data burst to which a hybrid automatic repeat request (HARQ) scheme is applied (HARQ data burst), a data burst to which the HARQ scheme is not applied (Non-HARQ data burst), or control information. Thus, the MSs must be previously aware of each MAP IE format in order to decode each MAP IE, and can discern each MAP IE from others by using a downlink interval usage code (DIUC) in the case of a downlink and by using an uplink interval usage code (UIUC) in the case of an uplink.
Further, as stated above, in the BWA communication system, data transmission is performed on a frame-by-frame basis, and each frame is divided into a downlink data transmission sub-frame and an uplink data transmission sub-frame. Here, the data transmission sub-frame is configured in a two-dimensional arrangement of frequency domain vs. time domain, and each two-dimensional arrangement is a slot corresponding to an allocation unit. That is, the frequency domain is divided in units of sub-channels, each of which is a bundle of sub-carriers, and the time domain is divided in units of symbols. Therefore, the slot represents a symbol region occupied by one sub-channel. Each slot is allocated to only one MS among MSs existing in one cell, and a set of slots allocated to the respective MSs existing in one cell is a burst. In this way, radio resources in the communication system are allocated in such a manner that the respective MSs use divided slots.
FIG. 1 illustrates the frame structure of a common IEEE 802.16e communication system.
Referring to FIG. 1, a frame is represented by symbols and sub-channels in time and frequency domains, respectively. The y-axis denotes a sub-channel which is a resource unit of frequency, and includes an N number of sub-channels from an s-th sub-channel to an (s+L)-th sub-channel. The x-axis denotes an OFDM symbol which is a resource unit of time, and includes an M number of downlink OFDM symbols from a k-th OFDM symbol to a (k+M)-th OFDM symbol and an N number of uplink OFDM symbols from a (k+M+1)-th OFDM symbol to a (k+M+N)-th OFDM symbol. Further, the frame includes a downlink sub-frame 100 and an uplink sub-frame 150, and a transmitter time guard (TTG) interval exists between the downlink sub-frame 100 and the uplink sub-frame 150.
The downlink sub-frame 100 includes a preamble field 111, a frame control header (FCH) field 113, a DL-MAP message field 115, a UL-MAP message field 117, and a plurality of downlink burst (DL-Burst) fields, that is, a first downlink burst field (DL-Burst #1) 119-1, a second downlink burst field (DL-Burst #2) 119-2, a third downlink burst field (DL-Burst #3) 119-3, a fourth downlink burst field (DL-Burst #4) 119-4, a fifth downlink burst field (DL-Burst #5) 119-5, a sixth downlink burst field (DL-Burst #6) 119-6, a seventh downlink burst field (DL-Burst #7) 119-7 and a eighth downlink burst field (DL-Burst #8) 119-8. The uplink sub-frame 150 includes a plurality of uplink burst (UL-Burst) fields, that is, a first uplink burst field (UL-Burst #1) 151-1, a second uplink burst field (UL-Burst #2) 151-2, a third uplink burst field (UL-Burst #3) 151-3, a fourth uplink burst field (UL-Burst #4) 151-4, a fifth uplink burst field (UL-Burst #5) 151-5, a sixth uplink burst field (UL-Burst #6) 151-6 and a seventh uplink burst field (UL-Burst #7) 151-7.
A transmission/reception period, that is, a synchronization signal for synchronization acquisition between a BS and MSs, which is called a preamble sequence, is transmitted through the preamble field 111. Further, basic information about sub-channels, ranging, modulation schemes, etc. is transmitted through the FCH field 113. A DL-MAP message is transmitted through the DL-MAP message field 115, and a UL-MAP message is transmitted through the UL-MAP message field 117.
The DL-MAP message field 115 includes a plurality of IEs, and the respective IEs include information on the downlink burst fields corresponding thereto, that is, information on the DL-Burst #1 119-1, information on the DL-Burst #2 119-2, information on the DL-Burst #3 119-3, information on the DL-Burst #4 119-4, information on the DL-Burst #5 119-5, information on the DL-Burst #6 119-6, information on the DL-Burst #7 119-7 and information on the DL-Burst #8 119-8.
The UL-MAP message field 117 includes a plurality of IEs, and the respective IEs include information on the uplink burst fields corresponding thereto, that is, information on the UL-Burst #1 151-1, information on the UL-Burst #2 151-2, information on the UL-Burst #3 151-3, information on the UL-Burst #4 151-4, information on the UL-Burst #5 151-5, information on the UL-Burst #6 151-6 and information on the UL-Burst #7 151-7. Each corresponding data burst is transmitted through the DL-Burst #1 119-1 to the DL-Burst #8 119-8, and each corresponding uplink data burst is transmitted through the UL-Burst #1 151-1 to the UL-Burst #7 151-7.
An MS receives the DL-MAP message and the UL-MAP message, and decodes the received DL-MAP and UL-MAP messages to thereby detect an IE indicating information on resources allocated thereto, that is, a MAP IE. Through the detected MAP IE, the MS can find out a resource region allocated thereto. Here, each IE included in the DL-MAP message represents the allocated region by indicating its starting points and sizes in time and frequency domains, and each IE included in the UL-MAP message represents the allocated region by indicating the starting point and size of a multiple of a slot. Here, the slot refers to a minimum resource allocation unit consisting of sub-channels and symbols.
Therefore, when the MS receives the DL-MAP message, it successively decodes MAP IEs included therein. If the MS detects a MAP IE allocated thereto in the course of decoding, it can find out the position of resources allocated thereto by using position information of the detected MAP IE. Further, when the MS receives the UL-MAP message, the MS adds regions occupied by all MAP IEs before a MAP IE allocated to the MS is detected, and the position a MAP IE allocated to the MS is determined as the position of a region next to the added regions.
In this way, the IEEE 802.16e communication system allocates sub-channels to respective MSs in an uplink/downlink through a sub-channel allocation scheme using an adaptive modulation and coding (AMC) scheme (AMC sub-channel allocation scheme). Here, the AMC scheme is a scheme in which a modulation technique and a coding technique is adaptively changed according to wireless environments in order to improve data transmission efficiency, and a detailed description thereof will be omitted because it is well known in the art. Further, if the MS receives the UL-MAP message, it ascertains allocation information of a channel state information channel (CSICH) for transmitting its channel state information (CSI) to a BS, and transmits the CSI to the BS over the CSICH.
FIG. 2 illustrates a scheme in which an MS transmits its CSI to a BS over a CSICH in the IEEE 802.16e communication system.
Referring to FIG. 2, in the scheme of transmitting the CSI of an MS to a BS over an CSICH in the IEEE 802.16e communication system, each MS selects five sub-channels 201, 203, 205, 207, 209 having good channel conditions from among sub-channels allocated thereto, and transmits channel state values carried in the indexes of the selected sub-channels 201, 203, 205, 207, 209 to the BS. Neither information on the non-selected sub-channels is carried in their indexes nor is the information transmitted. More specifically, each MS measures channel states with respect to the BS, for example, measures carrier to interference and noise ratio (CINR) of respective sub-channels, selects five sub-channels 201, 203, 205, 207, 209 having good channel conditions from among the measured sub-channels, and then transmits the CSI of the selected five sub-channels 201, 203, 205, 207, 209 to the BS over the CSICH. However, the MS does not transmit the CSI of non-selected sub-channels.
With regard to this, when the CSI of the selected five sub-channels 201, 203, 205, 207, 209 are transmitted to the BS, there is a problem in that resources required for transmitting the CSI increase. Particularly, the greater the number of MSs provided with communication services from the BS, the greater the amount of data to be transmitted to the BS, that is, the greater the amount of feed back information, which results in lowering of the use efficiency of resource.